The invention relates to a fitting made of weldable, thermoplastic material and having a modular construction, containing a plurality of elements, at least one main element and at least one connection element.
Fittings are understood to be pipeline connectors which connect pieces of pipe to one another and also perform further functions in the process, e.g. changing the direction of the pipe sections which are to be connected. In order to lay a pipeline, it is necessary to use fittings, be this in order to realize branches in the pipelines or in order to deflect the lines by installing bends therein. As far as plastics pipelines are concerned, such fittings are usually produced by injection molding. For reasons relating to cost, injection molding is an ideal method of producing fittings as long as large numbers are required. Injection molding requires an injection mold, which is very complex to produce and is therefore costly. In order to ensure that the injection mold pays for itself, it is therefore necessary to produce large numbers of parts. It is only in this way, by providing large numbers of the parts which are to be produced, that the mold cost per individual part can be kept to a very low level. However, in the case of small numbers, the price for an individual part would be rendered so high by the additional payback costs of the injection mold that an individual part would no longer be affordable or this would no longer be a tenable option for the manufacturers of such parts, since the parts would not cover the production costs. Such fittings usually have large diameters, which are only seldom used.
It is known for it to be possible for such large-dimension fittings made of weldable plastics to be welded together from pipe segments, that is to say that the fitting comprises a plurality of individually cut-to-shape pipes, which are then welded together. For example for a tee fitting, existing pipes are split and/or cut to shape such that two pipes have 45° miters cut over half their circumference at one end in each case, these miters are then welded together, and the pipe which is used as the centerpiece of the tee fitting is first of all mitered to a point in order to be welded to the two pipes offset at 90° in the direction of the centerpiece. This gives rise to a weld seam which runs in the corners of the tee fitting. A fitting produced in this way is not suitable for withstanding nominal pressures since the seams in these positions are exposed to extremely high loading and would therefore not meet the requirements. In addition, production is very time-consuming on account of the corresponding preparation of the pipes which are to be welded.
U.S. Pat. No. 3,873,391 discloses a method of producing a plastics pipe fitting, for example a tee fitting. The method comprises the shaping of the plastics pipe sections by contours with complementary miters being produced and by the desired fitting being formed by virtue of the complementary plastics pipe sections being joined together. The peripheries are temporarily secured in the assembled position by, for example, adhesive. A liquid mixture, for example polyurethane elastomer, is then applied, preferably by spraying, to the outer surface in the region of the mitered contour. Setting or curing gives rise to a tough, but slightly elastic layer, which holds the plastics pipe sections together.
Such fittings are disadvantageous, on the one hand, on account of their high-outlay production and, on the other hand, on account of them not being suitable for high pressures as a result of the methods used for connecting the plastics pipes.
It is an object of the invention to propose a plastics fitting, and an associated production method, which is suitable, even in terms of cost, for a small-batch production and meets the requirements of the compressive strength and the surface nature in the pipeline interior.